1. Field of the Invention
This invention relates to a novel synthetic porous crystalline material designated as "MCM-21", to a method for its preparation and to its use in catalytic conversion of organic compounds.
2. Description of the Prior Art
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, crystalline microporous oxides having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline porous oxides. These materials can be described as a rigid three-dimensional framework of oxides such as SiO.sub.4 and AlO.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total non-oxygen atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra may be balanced by the inclusion in the crystal of a cation, for example an alkali metal or an alkaline earth metal cation. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchanqe, it has been possible to vary the properties of a given crystalline porous oxide by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. The zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite A (U.S. Pat. No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4 (U. S. Patent 3,314,752), zeolite ZSM-5 (U.S. Pat. No. 3,702,886), zeolite ZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U. S. Patent 3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983), ZSM-35 (U.S. Pat. No. 4,016,245), ZSM-38 (U.S. Pat. No. 4,046,859), and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.
Aluminum phosphates are taught in U.S. Pat. Nos. 4,310,440 and 4,385,994, for example. Aluminum phosphate materials have electroneutral lattices and, therefore, are not useful as ion-exchangers or as catalyst components. Microporous aluminum phosphates have a composition typified as: EQU xR:Al.sub.2 O.sub.3 :(1.0.+-.0.2) P.sub.2 O.sub.5 :YH.sub.2 O
wherein R is an organic amine or quaternary ammonium salt entrapped within the aluminum phosphate and playing a role as crystallization template, x and y representing the amounts of R and H.sub.2 O needed to fill the microporous voids. Because of the aluminum/phosphorus atomic ratio of these materials being about unity, they display virtually no ion-exchange properties, the framework positive charge on phosphorus being balanced by corresponding negative charge on aluminum: EQU AlPO.sub.4 =(AlO.sub.2.sup.-) (PO.sub.2.sup.30)
U.S. Pat. No. 4,440,871 teaches material called silicoaluminophosphate without non-aluminum metal.
The phosphorus-substituted zeolites of Canadian Patent Nos. 911,416; 911,417 and 911,418 are referred to as "aluminosilicophosphate" zeolites. Some of the phosphorus therein appears to be occluded, not structural. These latter materials containing silicon, aluminum and phosphorus are characterized by the general formula: EQU M.sub.(x-y) :x(AlO.sub.2.sup.-):(SiO.sub.2):Y(PO.sub.2.sup.+):zH.sub.2 O
wherein M is a monovalent cation, x is approximately 0.125-1.5, y is 0.05 -1.0 and z is the number of hydration water molecules. Structural replacement of silicon with phosphorus has been realized in materials called silica clathrates (West Germany Patent No. 3,128,988).
U.S. Pat. No. 4,363,748 describes a combination of silica and aluminum-calcium-cerium phosphate as a low acid activity catalyst for oxidative dehydrogenation. Great Britain Patent No. 2,068,253 discloses a combination of silica and aluminum-calcium-tungsten phosphate as a low acid activity catalyst for oxidative dehydrogenation. U.S. Pat. No. 3,801,704 teaches an aluminum phosphate treated in a certain way to inpart acidity. U.S. Pat. No. 4,228,036 teaches an alumina-aluminum phosphate-silica matrix as an amorphous body to be mixed with zeolite for use as cracking catalyst. U.S. Pat. No. 3, 213,035 teaches improving hardness of aluminosilicate catalysts by treatment with phosphoric acid. The catalysts are amorphous.
U.S. Pat. No. 2,876,266 describes an active silicophosphoric acid or salt phase of an amorphous material prepared by absorption of phosphoric acid by premolded silicates or aluminosilicates.
Other teachings of aluminum phosphates and their preparation include U.S. Pat. Nos. 4,365,095; 4,361,705; 4,222,896; 4,210,560; 4,179,358; 4,158,621; 4,071,471; 4,014,945; 3,904,550 and 3,697,550. Since their neutral framework structure is void of ion-exchange properties, they are used as catalyst supports or matrices.
The crystalline material synthesized hereby has a novel structure. It is a molecular sieve exhibiting ion-exchange properties and is easily and conveniently converted to material having intrinsic catalytic activity.